Graft polymers are well known. For example, U.S. Pat. No. 3,760,034 to Critchfield et al. generally discloses certain graft copolymers of lactone polyesters. More particularly, the Critchfield patent specifically teaches that such graft copolymers can be obtained utilizing lactone polyesters and ethylenically-unsaturated monomers. Along these lines, other investigators have reported development of a procedure for grafting caprolactone onto a low molecular weight hydroxy acrylic polymer in the presence of a dibutyltin oxide catalyst. (See Journal of Coatings Technology, October 1982, Volume 54, No. 693, pages 77-81.)
Briefly, a graft copolymer comprises at least one main chain and a plurality of side chains attached to each such main chain. U.S. Pat. Nos. 3,892,714 and 4,005,155, both to Sampson et al., disclose certain polymeric compositions comprising main chains, side chains attached thereto, and crosslinking units between side chains. Sampson et al. teach that the main chains consist of a copolymer of two or more ethylenically-unsaturated monomers (at least one of which contains hydroxyl groups) wherein the side chains consist of lactone chains attached to the hydroxyl groups. Still more particularly, Sampson et al. disclose in the '714 patent that the crosslinking units consist of a polyisocyanate such as di-isocyanate. In the '155 patent, Sampson et al. disclose that the crosslinking units consist of an amino resin such as urea formaldehyde, melamine formaldehyde, or benzoguamine formaldehyde.
Typically, a graft polymer is produced in a sequential manner, utilizing a series of steps. For example, one such polymer is first formed, utilizing a particular reaction step. Thereafter, the thus-formed polymer is utilized as a so-called "main chain" onto which certain side chains can be grafted. In particular, such a thus-formed polymeric main chain typically has side chains grafted thereonto via a subsequent reaction step. One method for forming such a graft polymer typically requires utilizing separate reaction vessels to accomplish the separate reaction steps. (See, e.g., Example 1 of U.S. Pat. No. 3,760,034 to Critchfield et al.)
It is also fairly typical, moreover, in conventional graft polymer-manufacturing processes (such as those mentioned above), to utilize a catalyst to effect the main-chain and/or the side-chain formation of the desired polymer product. See, e.g., British Pat. No. 1,443,073 to Bayne et al., which teaches that use of stannous octoate as catalyst is "essential" to achieve reaction of three ingredients in a single step. Also worthy of note in this regard is U.S. Pat. No. 4,082,816 to Fisk et al., a patent generally directed to the preparation of a caprolactone-modified acrylic polymer, wherein the inventors particularly point out that the polymerization medium "should include" a polymerization catalyst for the caprolactone. (See also U.S. Pat. Nos. 3,892,714 and 4,005,155, both to Sampson et al., which disclose using a catalyst such as an organic peroxygen compound, an organic peroxide, an organic hydroperoxide, or an azo compound such as 2,2'-azo bis-2-methyl propionitrile.) To use a catalyst to effect simultaneous main-chain as well as side-chain formation, however, is undesirable for a variety of reasons.
Generally, a catalyst is chosen so as to beneficially and optimally effect reaction of one particular catalytically-reactable ingredient. One disadvantage of utilizing such a catalyst to effect two or more chemical reactions via a one-step method is that such a catalyst, typically utilized to effect either the main-chain "formation" polymerization reaction or the side-chain "grafting" polymerization reaction, undesirably affects the reaction mechanism (or mechanisms) that it does not optimally effect. The reason is that certain catalysts, although necessary to cause one of these reactions to occur, can and typically do undesirably interfere with the other reaction. Such interference, in turn, may result in the production of a polymer having undesirable properties, may result in the production of an undesirable polymerization by-product that needs to be separated from the desired polymer product, or may give rise to some other unforeseen and undesirable result. For example, Brode et al. [J. Macromol. Sci.-Chem., A6(6), pp. 1109-1144 (1972)] present data (at pages 1116-1119), suggesting that utilization of certain catalysts renders certain polymer products thermally unstable.
More particularly, however, utilization of a specific catalyst, to effect desired side-chain "grafting" formation, may cause undesired side-chain formation such as so-called "transesterification" to take place at the main-chain portion of the polymer. Transesterification, in turn, generally results in the occurrence of undesired crosslinking taking place during the side-chain "grafting" step. This is undesirable, as was briefly indicated above, because such crosslinking tends to increase the viscosity of the thus-produced graft polymer, and may even result in the gellation of the polymer product or products so produced, which is generally undesirable.
Accordingly, from an engineering standpoint, from a capital-investment standpoint, from a manpower-utilization standpoint, from an equipment-scheduling standpoint, and, e.g., from a product-manufacturing standpoint, it would be not only economical but also desirable to be able to effect substantially simultaneous main-chain formation as well as side-chain formation of such a polymer, because the substantially simultaneous chain-formation mechanisms would enable utilization of a single reaction vessel.
It would further be desirable not only to produce such polymer products in a single reaction vessel but also to so produce such polymers without requiring the presence of a catalyst.
We have discovered that a graft polymer of this type--that is, a graft polymer comprising at least one polymeric main chain and a plurality of polymeric side chains attached to the main chain--can be produced in accordance with the principles of our novel process disclosed hereinbelow. One embodiment of such a process, for example, utilizes a single reaction vessel in which the graft polymer formation occurs. That is, the main chain and the side chains of the graft polymer are formed substantially simultaneously within the single reaction vessel.
We have also discovered that the principles of our particular invention can satisfactorily and effectively be practiced without the need for a catalyst. Indeed, no graft polymer herein disclosed was made in the presence of a catalyst.